configure: Begin prettifying configure.ac

Issue #54.
configure: Export package versioning

Issue #54.
configure: Double up newlines between sections

Issue #54.
configure: Add compiler section

Issue #54.
configure: Complete section structure

Issue #54.
configure: Add TODO note

Issue #54.
configure: Prefix version macros with 'pipdb_'

Issue #54.
configure: Double newline between sections

Issue #54.
configure: Output package name and version in summary

Issue #54.
configure: Remove top newline

Issue #54.
configure: Remove broken dnl comments

Issue #54.
configure: Set HAVE_HTTPD shell var

Issue #54.
configure: Export apache2 location

Issue #54.
configure: Define HAVE_WWW_ROOT

Issue #54.
configure: Beautify configure summary

Example configure summary:

  pip-db - 0.0.1
  --------------

   • Global:
          httpd:                          /usr/sbin/apache2
          httpd root:                     /var/www/
          mysql:                          no

   • Features:
          Content hashing algorithm:      md5sum
          Content hashes length:          8

   • Build options:
          Build directory:                /home/chris/pip-db/build/www/

   • Extra:
          Building extra documentation:   yes

Issue #54.
configure: Minor refactors

Issue #54.
configure: Refactor node optimist package check

Issue #54.
configure: Use 'yes/no' for booleans, not 'true/false'

Issue #54.
configure: Use $(cmd) not `cmd`

Issue #54.
configure: Use m4 defines not shell vars

Issue #54.